HomeMy WebLinkAboutValero Station & Minimart Closure Summary 9-17Valero Station & Minimart - 2 - 18 October 2017 Bakersfield, Kern County Closure Summary
two feet beneath the USTs, and from 76 – 760 mg/kg were detected in three samples from six feet below the USTs. Total petroleum hydrocarbons oil-range (TPHo) was detected to a
maximum concentration of 270 mg/kg. TPHd was also detected at low concentrations in two samples beneath a diesel fuel dispenser. The City of Bakersfield Fire Department (BFD) referred the release to the Central Valley Water Board for regulatory oversight, as BFD no longer provides oversight for investigation and cleanup of UST releases Soil Investigation
Four direct-push soil borings were advanced to a maximum depth of 50 feet below ground surface (bgs) on 10 April 2017. Boring AEC-1 was advanced in the area of highest hydrocarbon
concentrations beneath the northern 4,000-gallon UST. The remaining three borings, AEC-2, AEC-3 and AEC-4, were from 10 – 30 feet southeast, south and north of AEC-1 respectively, to delineate the lateral extent of the release.
Soil samples were collected at five-foot intervals beginning at 10 feet bgs in AEC-1 and AEC-4, and beginning at 5 feet bgs in the other borings. The samples were screened in the field for
volatile organic vapors with a photo-ionization detector (PID). Selected samples, including the two deepest consecutive samples, were analyzed for total petroleum hydrocarbons as carbon chain (TPH-cc) by EPA Method 8015M; and full-scan volatile organic compounds (VOCs) by EPA Method 8260B. Analytical results indicated concentrations of diesel range organics from 1,100 – 5,100 mg/kg in the samples collected from 20 – 40 feet bgs from AEC-1, and at less than 40 mg/kg in the sample from 10 feet bgs, and in the two deepest samples from 45 and 50 feet bgs. Gasoline range organics were detected at concentrations from 110 – 1,600 mg/kg, but were not detected in the two deepest samples. Low toluene, ethylbenzene and xylene concentrations were detected in some of the samples from AEC-1, and oil range hydrocarbons were also detected.
Low concentrations of diesel and gasoline constituents were detected in some of the samples collected from AEC-2 through AEC-4. The highest concentrations were from AEC-4, with TPHd and TPHg as high as 490 and 17 mg/kg, respectively. Benzene and the fuel oxygenates were not detected in any of the samples collected.
Ethylbenzene and naphthalene were detected in samples from 0 – 10 feet bgs at maxima of 3.9 and 1.4 mg/kg, respectively. The consultant concluded that hydrocarbons from the UST release were present in soil to a depth of approximately 50 feet bgs, and within a surface area of approximately 20 x 20 feet. Vertical migration was limited by the sand/clay silt zone noted from 35 – 50 feet bgs. Approximately 1,600 pounds of diesel range hydrocarbons were estimated to remain in soil. Groundwater depth is at approximately 200 feet bgs, resulting in an approximate 150-foot buffer zone present between the release and groundwater. The consultant recommended case closure and Staff concurred. Sensitive Receptors The concrete-lined East Branch Canal borders the site on the south and is less than 100 feet from the release. California Water Service Company Well #75 is approximately 600 feet east of the Site. The fuel
oxygenate methyl tertiary butyl ether (MTBE) was detected in Well #75 at 1.4 µg/L during 2000, after which the well became inactive. Other wells were not identified within 1,000 feet.
Valero Station & Minimart - 3 - 18 October 2017 Bakersfield, Kern County Closure Summary
Low-Threat Underground Storage Tank Case Closure Policy Evaluation The subject UST release satisfies all relevant General Criteria: a. The release is within the service area of a public water system; b. the release consists only of petroleum; c. the (“primary”) release from the UST system has been stopped; d. free product is not present. The criteria for free product removal to the maximum extent practicable is not relevant; e. a Conceptual Site Model has been completed. f. secondary source has been removed to the extent practicable. An undocumented mass was removed during the UST removal activities. The consultant estimated that 1,600 lbs. of source mass remains, which is expected to degrade naturally;
g. soil has been tested for methyl tertiary butyl ether (MTBE), in accordance with Health and Safety Code section 25296.15; and h. nuisance as defined by Water Code section 13050 does not exist.
The subject UST release satisfies the relevant Media-Specific criteria:
1. Groundwater – The release has not affected groundwater - the criteria are not relevant. 2. Petroleum Vapor Intrusion to Indoor Air - The Site is an active commercial petroleum fueling facility, and the release is therefore not required to satisfy the Policy’s Media-Specific Criteria. The Policy states that exposure to petroleum vapors associated with historical fuel system releases are comparatively insignificant, relative to exposure from small surface spills and fugitive vapor releases that typically occur at active fueling facilities. 3. Direct Contact and Outdoor Air Exposure - Benzene, ethyl benzene, and naphthalene concentrations exceeding human health screening levels listed in Table 1 were not detected in areas of potential shallow soil contamination during previous investigation. The subject UST release satisfies criteria in the Low Threat Case Closure section: a) Municipal and county water districts, water replenishment districts, special act districts with groundwater management authority, agencies with authority to issue building permits for land affected by the unauthorized release, and the owners and occupants of the property affected by the unauthorized release, and owners and occupants of all
parcels adjacent to the impacted property have been notified of the proposed case closure and were provided a 60 day period to comment. A Public Notice of the proposed case closure was mailed to the parties and posted on the Central Valley Water Board’s website on 1 August 2017. No comments adverse to closure were received. b) No groundwater monitoring or remediation wells were installed. The requirement to destroy wells is not relevant. c) An inspection verified that waste piles, drums, debris and other investigation derived materials have been removed from the property and properly managed in accordance with regulatory agency requirements. Conclusions
Source hydrocarbon mass has been removed to the extent practicable. The release lacks the mobility to reach groundwater, which is very deep. The remaining effects of the UST release
are unlikely to threaten the present use of surface water, groundwater and public health, and should continue to degrade naturally. Case closure is in accordance with the State Water Resources Control Board’s Low-Threat Underground Storage Tank Case Closure Policy, and
the case closure requirements of Health and Safety Code section 25296.10. I recommend that an underground storage tank release case closure letter be mailed to the responsible parties.